Hydrocarbon fluids, during the production and transportation from reservoir to the surface and onward to refinery undergo pressure and temperature changes. These changes along with changes in operating conditions can lead to destabilization and precipitation of various components in the fluids (e.g., paraffins, asphaltenes, scales). Under favorable conditions, these precipitated components can cause significant flow assurance challenges including, but not limited to, an increase in fluid viscosity and deposition of solids on pipeline surfaces. These, in turn, can then cause numerous operational challenges such as flow restriction in a pipeline, increased solids during pigging operations leading to decreased cleaning efficiency, or higher pipeline back pressure leading to lower throughput. Various thermal, mechanical and chemical methods are used to prevent and mitigate the precipitation and deposition of these components and to subsequently avoid costly delays due to their interference in the production and transportation process. These remedial methods include pigging or scraping, insulating equipment and flow lines to prevent loss of heat, applying heat by means of a heated liquid (e.g., hot oil or hot water), using a heat generated reaction, or the application of inhibitors, dispersants or solvents.
Paraffin precipitation and deposition and its effect of fluid flow in a pipeline remains one of the biggest challenge in the oilfield industry. Precipitation of paraffin (CnH2n+2) from hydrocarbons is a function of primarily temperature, however there are other parameters, such as pressure, that affect the solubility of paraffin in hydrocarbon fluids and can cause its precipitation. These precipitated paraffins, under favorable conditions tend to form deposits inside pipelines, vessels and other oilfield equipment causing several problems such as reduction in the flow, higher back pressures, increased fluid viscosity, higher solids in the fluid leading to stable emulsions and oil water separation problems. To overcome these challenges, various thermal, mechanical and chemical methods are used in the oilfield industry including pigging, scraping, hot oiling and using paraffin inhibitors, pour point depressants, paraffin dispersants, paraffin solvents and combinations thereof.
Paraffin inhibitors, typically crystalline/amorphous polymers, also known as wax crystal modifiers, are used in oil field industry to delay the onset of wax precipitation in hydrocarbon fluids and to mitigate the extent of wax deposition on the metal surfaces. These polymers, usually formulated in aliphatic or aromatic solvents, are injected above the wax appearance temperature (“WAT”). WAT is defined as the temperature at which a detectable amount of a solid phase forms upon cooling in the time frame of the measurement at a given pressure. A part of the wax inhibitor, which co-crystallizes with the paraffins has a structure that is similar to the waxes and is nonpolar is nature. There is typically a polar component present in the structure which limits the degree of co-crystallization. The paraffin inhibitors/wax crystal modifiers interfere with the wax crystallization by modifying the wax crystal morphology. The ill formed crystal (also called a malcrystal) cannot form networks thereby preventing deposition of wax on the pipeline surface.
Paraffin inhibitors/wax crystal modifiers are usually polymers that are formulated in solvents (aliphatic or aromatic) and, typically, polymers exhibit limited solubility in these solvents. Solubility of these polymers in the solvents also decreases dramatically at low temperatures which significantly limits the amount of polymer that can be incorporated into a solution at low temperature. In a deep-water or in a low temperature application, where it is important for the inhibitor solution to remain stable at the application temperature, only very dilute solutions of the wax crystal modifier/paraffin inhibitor can be formulated and applied.
Various techniques have been used to improve low temperature stability of wax crystal modifiers/paraffin inhibitors. This includes dilution, addition of surface active agents, producing the polymers in an emulsion or a dispersion form.